Microelectromechanical systems (MEMS) devices are employed as actuators, switches, and sensors (e.g., inertial sensors, pressure sensors, etc.) in various different applications. For example, many electronic devices utilize MEMS capacitive pressure sensors to detect changes in the pressure of a surrounding fluid, such as air. By common design, a MEMS capacitive pressure sensor functions by measuring the deflection of at least one flexible polysilicon diaphragm, which encloses a hermetically-sealed cavity containing a known reference pressure. The reference pressure acts on an inner face of the flexible polysilicon diaphragm, while the opposing face of the diaphragm is exposed to the fluid for which pressure measurements are taken. During operation of the MEMS sensor, the diaphragm deflects with variations in the external pressure and the corresponding variations in the pressure differential across the body of the diaphragm. An electrode (commonly referred to as the “bottom plate”) is provided below the diaphragm and is separated therefrom by a vertical gap. As the flexible membrane is also fabricated from an electrically-conductive polysilicon material, the membrane serves as a top plate forming a capacitive coupling with the bottom plate. This capacitance varies with deflection of the electrically-conductive diaphragm toward or away from the bottom plate. Thus, by measuring changes in this capacitance, variations in the external pressure acting on the exposed face of the diaphragm can be determined.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction and may omit depiction, descriptions, and details of well-known features and techniques to avoid unnecessarily obscuring the exemplary and non-limiting embodiments of the invention described in the subsequent Detailed Description. It should further be understood that features or elements appearing in the accompanying figures are not necessarily drawn to scale unless otherwise stated. For example, the dimensions of certain elements or regions in the figures may be exaggerated relative to other elements or regions to improve understanding of embodiments of the invention.